I believe that you need to slow things down a bit and get out of your muscle car, and look for the best quality you can afford.
1. Speakers are the heart of the system. A cheap A/V receiver with cheap speakers sound poor - no matter what. A cheap receiver with decent speakers can sound really good. I experienced this first hand when I disconnected my HTIB speakers from a $300 Kenwood setup and replaced them with a few grand in Definitive Technology speakers. The actual volume doubled - at least.
2. Your A/V receiver already has power inside of it. You can't add to it by putting another amp in-line, and odds are good that you don't need it anyway. If you have good speakers, you will have solid performance from that receiver.
3. If you want more power, you have speakers that are poor and inefficient, and can handle more power, then adding an external amp is fine, but you must your line level outputs from the A/V receiver to the amplifier. Look at the photos of the back of an amp and you will see that they only have RCA inputs or (sometimes) balanced audio inputs. Not speaker level inputs.
In all this, you still have to consider how good you want the audio to sound. Loud is easy and cheap - give me an air horn. Pleasant and loud is expensive. Pleasant and 'reasonable' is not terribly expensive and is a excellent way to go.
Now get back in your muscle car and drive awa... ooops - it just broke down again.